Manufacture of diolefins



June 18, 1946. FREY MANUFACTURE OF DIOLEFINS Filed Feb. 16, 1942 3 Sheets-Sheet l 65k hm H EEG: w u

EESOP UZFE Ekm OF 9 5 mm u ommmwoza INVENTOR FREDERICK E. FREY BY I 2 a 5 A RN;

832] NViNBdECI I Patented June 18, 1946 MANUFACTURE OF DIOLEFIN S Frederick E. Frey, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application February 16, 1942, Serial No. 431,152

1 Claim. 1

This invention relates to the production of conjugated diolefins, and more specifically, to the utilization of amylenes as a source of diolefins.

Butadiene and related diolefins have been found in numerous instances among the products of low-pressure pyrolysis of various simple hydrocarbons, including both parafllns and olefins. In general, the diolefin yields reported in the literature are low. However, I have found as the result of numerous experiments, that enhanced yields of diolefins are obtained when the pyrolysis is conducted at a high temperature, with the time of heating limited to values small enough so that part of the hydrocarbon being pyrolyzed survives the heating unchanged. The yield of diolefins is further improved if the pyrolysis is conducted at low pressure or in the presence of diluents such as steam, flue-gas, methane and the like.

I have found that under suitable conditions of low pressure, high temperature and very short heating time good yields of diolefins containing four and five carbon atoms per molecule can be obtained from certain of the amylenes, namely, pentene-2 and trimethylethylene. while the yields are much lower from the other amylenes occurring in cracked material in appreciable amounts, i. e. unsymmetrical methylethylethylene and pentene-l.

The objects of my invention are:

1. To eifect the pyrolytic conversion by a recycle process of suitable amlyenes into useful and substantial yields of butadiene and pentadienes.

2. To utilize a hydrocarbon fraction containing five carbon atoms per molecule and containing a considerable proportion of amylenes such as the C fraction obtained from typical cracking still gasoline.

3. To produce, by an economical separating means, a conversion feed stock rich in the preferred olefins and differing in olefin make-up from such a C5 fraction.

4. To provide an advantageous combination of such separating means with conversion means for producing butadiene and pentadienes.

5. To produce aliphatic conjugated diolefins and other useful byproducts.

6. To provide a new process of cracking pentene-2 and/or trimethylethylene to diolefins.

Numerous other objects will more fully appear hereinafter from a consideration ofthis description taken in conjunction with the accompanying drawings wherein:

equipment useful for carrying out the recovery of pentene-2 and trimethylethylene from an amylene-containing refinery C5 fraction to be passed to the pyrolysis step.

Fig. 2 is a modification of Fig. 1 showing fractionation of the C5 fraction before entering the solvent extraction unit.

Fig. 3 portraysdiagrammatically one form 01 equipment for carrying out the pyrolysis of the desired amylenes.

The economical and efllcient production of allphatic conjugated diolefins, in particular butadiene, piperylene and isoprene, which are raw materials for the production of synthetic rubber, from readily available hydrocarbons of petroleum origin, is a serious problem, and one which has not to my knowledge been entirely satisfactorily solved. My invention seeks to provide a commercially feasible solution to this problem.

I use amylenes as the starting material for my process. Usually I take a refinery C5 stream containing pentanes and pentenes, although it may comprise preponderantly or consist essentially of pentenes. Higher and lower parafilns and olefins may also be present in the stream. I

- prefer to first treat this stream so as to eliminate such higher or lower parafilns or olefins, if present.

The fairly pure C5 stream may be subjected to catalytic isomerization to increase the concentration of pentene-2 and also trimethylethylene therein. This step converts pentene l largely to pentene-2 and also converts unsymmetrical amylone to trimethylethylene. Thus the concentration of the desirable high boiling point amylenes is increased, at the expense of the undesirable low boiling point amylenes.

The isomerization step per se does not constitute my invention. The details of eifecting this isomerization are well understood by and will be obvious to those skilled in the art in the light of this disclosure taken in conjunction with the prior art.

Where the content of the desirable amylenes in the available C5 or pentene stream is sufiiciently high to make solvent extraction thereof economically feasible, the isomerization step may be omitted, and the feed subjected to solvent extraction.

In some cases a feed is available which is sufficiently rich in the desired amylenes (pentene-2 and/or trimethylethylene) to use as cracking feed directly or after fractionation to remove C3 an lighter and C6 and heavier if present.

Fig. l portrays diagrammatically. one form 01'55 The isomerization eflluent or, where isomerihigh yields.

zation is omitted, the substantially pure C5 stream free from lighter and heavier ydrocarbons, may next be subjected to selective solvent extraction with a polar solvent capable of exerting a preferential solvent action upon oleflns as distinguished from paramns and upon the desirable higherboiling amylenes (pentene-2 and/or trimethylethylene) as distinguished from the undesired low-boiling amylenes .(pentene-l and unsymmetrical amylene) Upon stripping the separated polar solvent there is recovered a cracking feed concentrate rich in or consisting essentially. of pe'ntene-Z and/or trimethylethylene.

The isomerization step described above is desirable for several reasons. It lowers the overall cost of operating the process and of producing diolefins, makes a larger volume of the; desirable amylenes available for cracking and lowers the unit cost of solvent extraction ofthe high-boiling amylenes because of their higher concentration in the feed to the extraction unit.

The cracking feed thus prepared is now subiected to cracking in such manner as to convert the pentene-2 and trimethylethylene content thereof largely to diolefins, especially butadiene 4 about 45%. These are materially higher than the yields obtainable with any prior art process .of cracking these pentenes, with which I am familiar.

A charge stock which comprises a hydrocarbon fraction containing five carbon atoms per molecule and containing a considerable proportion of amylenes, such as the (Is-fraction obtained from typical cracking-still gasoline, enters the system through pipe I, controlled by valve 2, and passes to a debutanizer 3. The C4-hydrocarbons and lighter products are recovered overhead and are withdrawn from the system through pipe 4 and and pentadiene. The dehydrogenation of trimethylethylene gives largely isoprene while the cracking of pentene- 2 gives mainly butadiene and some piperylene. Some cyclopentadiene may also be frequently formed in the cracking step.

The cracking may be carried out at a temperature above 700 0. up to 900 C.and preferably from about 750 C. to about 850 C. The specific cracking conditions, i. c. time-temperature relationship, are indicated below. The pressure may range from about 0.1 to about 2 atmospheres but is preferably substantially atmospheric.

The cracking may advantageously be conducted in a two-step manner, as described in the copending application of H. J. Hepp, Ser. No. 431,175 filed of even dateherewith, wherein the feed is first cracked under relatively mild conditions to selectively destroy pentene-Z, and the butadiene is recovered from the eiiluent, the C5 portion of the efiluent being then cracked under more drastic conditions to convert the trimethylethylene content thereof to isoprene.

The cracking of pentene-2 specifically is not claimed herein but is claimed in my copending application Ser. No. 431,151, filed of even date herewith.

By means of the present invention, exceptional yields of desirable diolefins are obtainable. The cracking conditions contribute largely to these Also the combination, cooperation, and inter-relation of the several steps of obtaining the concentrate rich in pentene-2 and/or trimethylethylene which is especially suited for cracking to the desirable diolefins, contribute very materially to the high yields of desirable diolefins based on the original amylene-containing raw material. I

The diolefins comprise largely butadiene and pentadienes. The pentadienes comprise mainly isoprene, some piperylenedepending on cracking conditions, and some cyclopentadiene which is undesirable. Pentene-2 gives mainly butadiene, some piperylene and perhaps some isoprene. Trimethylethylene gives mainly isoprene, some valve 5. The hydrocarbons which are higher boiling than the C r-hydrocarbons are recovered as kettle product and are passed through pipe 6, controlled by valve I, to depentanizer 8. The Cs-hydrocarbons and heavier products are recovered as kettle product and removed from the system through pipe 9, controlled by valve I0. The Cs-hydrocarbons are recovered overhead and are passed through pipe II, by means of valves I2 and I3 to solvent extraction unit I4.

If desired, a portion or all of the Cs-hydrocarbons may be passed, controlled by valve I3, from pipe II through pipe I5, by means of valve IE to an isomerization step. The purpose of this isomerization step is to effect conversion of pentene-l to. pentene-2. By means of heating arrangement II, the stream is heated to a temperature in the range of from about 150 to about 350 C. and passed to isomerization step I8. The stream is there contacted with a suitable catalyst such as phosphoric acid, aluminum sulfate, or the like, for a period of time, in the range of from about 2 seconds to about 3 minutes, sufflcient to effect substantial isomerization of pentene-l to pentene-2; there will be some conversion of unsymmetrical amylene to trimethylethylene.

A typical refinery Cs-fraction, such as that being charged to the isomerization step, would have about the following composition: pentene-l, 9%; pentene-2, 17%; trimethylethylene, 9%; unsymmetrical methylethylethylene, 5%; and the remainder predominantly pentanes. An isomerizer would effect such conversion that the ratio of.

pentene-l to pentene-2 in the isomerization effiuent would be about 1 to 10.

The efiuents from the isomerization step are passed through pipe I9, controlled by valve 20, to a fractionating step 2|. The Cs-hydrocarbons and heavier products are separated as kettle product and withdrawn from the system through butadiene, and occasionally some piperylene.

pipe 23, controlled by valve 24. Pentane-pentenes and any lighter hydrocarbons present are passed through cooler 22, which supplies a liquid condensate for reflux in column 2 I, pipe 26, valve 21 to pipe |I,.to be subjected to further separation steps.

The Cs-hydrocarbon fraction is next subjected to separation means in order to obtain concentrates of pentene-2 and/or trimethylethylene.

As shown in Figure 1, separation may be effected )y means of solvent extraction; the solvent extraction step may however, be preceded by a fractionation' step, as shown in Figure 2. In an alternative method trimethylethylene and cisand transpentene-Z may be separated from other pentanes and non-cyclic olefins present by means of azeotropic distillation employing acetaldehyde, propionaldehyde or other suitable materials as entrainers. This azeotropic fractionation may be preceded by a. simple fractionation to separate low-boiling pentane and pentenes, i. e. boiling be A low about 35 0. While this particular combi- Normal pentane is recovered overhead and withdrawn from the system through pipe 49, by means of valve 50. The solvent extract, containing pentene-2 and trimethylethylene, is Passed from the bottom of the tower through pipe 5|, controlled by valve 52, to stripping tower 53, which separation, the Cir-hydrocarbon fraction is passed from pipe ll to solvent extraction tower l4. Solvent, which may be any convenient selective solvent such as furfural is introduced into the extraction tower through pipe 28, and heating of the contents of the tower is effected by means of a heating coil 29. It may be necessary, in order to decrease or prevent loss of solvent overhead, to maintain "reflux" in theupper portion of the tower by a cooling coil or by recycling a is heated by coil 54. The stripped solvent is recovered as kettle product and is passed through pipe 5!, controlled by valve 58, through cooler 51 and recycled through pipe 41 to the solvent extraction tower. Pentene-Z and trimethylethylene are recovered overhead and passed through pipe 58, controlled by valve 59, to the cracking portion of the eflluent, which has been cooled by suitable means, to the upper portion of the tower. The extraction, in the case of furfural, is eflected at temperatures in the range of from about 50 to about 350 F., preferably in the range of from.

about '125 to about 225 F; and at pressures such that, at the temperatures prevailing, the vapor does not reach its dew-point. The temperature is not necessarily constant over the whole column, and the lowest temperature ordinarily should be suchthat dew-point conditions do not exist under the prevailing temperature and pressure conditions.

The fraction recovered overhead is composed predominantly of the pentanes, pentene-l, 2- methylbutene-i (unsymmetrical methylethylethylene), and 3-methylbutene-l. The components which are desired as feed for a cracking step, to be described later, are recovered along with the solvent as kettle product, and this mixture is passed through pipe 32, controlled by valve 33, to stripping tower 34. Heat is suppliedto the tower by means of a heating coil 85, and the stripped solvent is recovered as kettle product and passed through pipe 36, being withdrawn if desired through valve 31 but usually being passed to a cooler 38, wherein the stream is cooled to a desired temperature and recycled to the solvent extraction step with fresh solvent through pipe 29. Pentene-2 and trimethylethyleneare recovered overhead in concentrated form and are passed through pipe 39, controlled by valve 40, to the cracking unit shown in Figure 3.

When it is desirable to effect a preliminary separation before subjecting the Ca-fraction in line II to solvent extraction or azeotropic distillation, fractionation in a column of the conventional type is employed. The CB-hYdI'OCaI'bOH- I fraction is passed, as shown in Figure 2, through pipe I l to the fractionator 4 I, wherein the hydrocarbons are split into a low-boiling group and a high-boiling group. The cut-point for this operation, if made at about atmospheric pressure, should be in the range of 32 .to 36 C., preferably about 34 C. Isopentane, penetene-l, 2-

This stream or a portion of it may be returned to the isomerization step if desired by means not shown.

through the heating zone.

unit shown in Figure 3.

The cracking system as shown in Figure 3 will now be described. The pentene-2 and/or trimethylethylene concentrate from pipe 39 or from pipe 58 is passed to a heating system, which is herein represented by a convection coil, 98, and a radiation coil, 81. Steam or other stable, volatile diluent may be added to the charge stock; from pipe 62, steam etc., may pass through valve 63 directly to the convection coil 68 of the furnace or it may pass from pipe 92 through pipe 64, controlled by valve 86, to a separate heating coil, 66, and thence through pipe 61, by means of valve 68, to the convection coil 60 of the furnace or from pipe 81 through pipe 69, controlled by valve 18 to a radiation coil of the furnace. The charge stock is cracked in the furnace at temperatures above 700 0. up to 900 C., and preferably from about 750 C. to about 850 C. The heating time varies inversely with the temperature, decreasing as the temperature rises, and is adjusted to effect from about 30 to about 80 per cent decomposition of the less refractory pentene-2 per pass should be maintained in the lower part of the range when no diluent is used, or when the partial pressure of the amylenes is near or slightly above atmospheric pressure. The higher conversion may be employed when the pyrolysis is conducted at pressures below atmospheric, or when diluents such as steam are employed.

The eiiluents from the cracking step are passed from the furnace through pipe H, by means of valve 12, to cooler 13; the cooled eiiluents are passed to separation step 14. Polymers and water from the cracking step are withdrawn from the bottom of the separating column through pipe 15 by means of valve 16. The gases pass overhead through pipe 11, controlled by valve 18, to compressor 19, through pipe 88 to cooler 8| and the liquid products in the separator pass,from

the bottom of the column through pipe 86, controlled by valve 81, to pipe 88 and join the stream of any liquid products from separation step 14 which are being passed through pipe 98, controlled by valve 89 and pump 81a to the depropanizer. From the depropanizer, which is of the conventional type, propane and lighter gases are separated overhead and are withdrawn from the system through pipe 9|, controlled by valve 92. Other means equivalent in function to elements 14, 83, and 98 may be used, if desired.

The kettle product from the depropanizer 98 passes through pipe 93, controlled by valve 94,

t to a debutanizer. 85. In this unit, the Ci-hydro- The decomposition the butadiene may be separated from the other hydrocarbons by formation of the sulfone by reaction in unit 98 with S: introduced via line 06A. The butadiene sulfone is withdrawn from the system through pipe 09, by means of valve I00, and the remaining ci-hydrocarbons pass from the purification step through pipe IOI to be recycled to the cracking step through valve I02 and pipes 39 or 58 or withdrawn from the system through pipe I03, controlled by valve I04.

The kettle product from debutanizer 05 is withdrawn and passed through pipe I05, by means of valve I06, to depentanizer I07. The kettle product from this unit is withdrawn from the system through pipe I00 by means of valve I09. The cs-hydrocarbons pass overhead through pipe IIO, controlled by valve H3, and are subjected to a purification unit H4, such as sulfone formation, to separate the dioleflns. SO: may be introduced to unit 4 via line H2. Pentadiene sulfones are withdrawn through pipe H5, by means of valve H6, and the unreacted Ola-hydrocarbons are passed overhead through pipe I" and, through valve I I I, recycled to the cracking step.

In the process described in connection with Figure 3, the diolefins are recovered by reacting with sulfur dioxide. The monosulfone thereby formed may be separated from the unreacted products by decantation and/or distillation, and the dlolefin regenerated by heating the monosulfone to temperatures above about 80 C. and preferably above about 120 C. The reaction between diolefins and sulfur dioxide may suitably be conducted in the. dense phase at temperatures in the range of from about 30 to about 180 C., and preferably in the range of from about 100 to about150 C. Inhibitors such as pyrogallol, phenyl-beta-naphthylamine, etc., may be employed in the low temperature range to avoid the formation of insoluble, refractory polysulfones which do not regenerate the diolefln readily, but inhibitors are not necessary at temperatures above about 100 C., as polysulfones are formed only in small amount, if at all, at these temperatures. The time required to complete the sulfone reaction varies inversely with the temperature, from several days at 30 C. to about one-half to two hours at 150 C. The amount of sulfur dioxide used may be in the range of from about 2 to about 20 moles per mole of diolefin. The reaction is kinetically oi the second order, and the time required is decreased as the amount of sulfur dioxide is increased.

While I have shown separate diolefln recovery systems on both the butadieneand pentadienecontaining streams; these steps may be combined,

. the butadiene and pentadiene sulfones being recove'red together. Upon regeneration butadiene may be readily separated from pentadienes if desired by fractionation.

Other methods of recovery of butadiene and pentadienes may be used if desired. In alternative methods of recovering dioleflns and recycle stocks to those shown in Figure 3, butadiene may be recovered from the (Ti-hydrocarbons passing through pipe 06 by fractional distillation, wher in butene-l and isobutylene are separated in a first fractionator, following which butadiene is separated from butene-2. Or the separation may be performed in a single step using an entrainer such as acetaldehyde. Or another method of separation is by means of selective solvent extraction, using for example, furfural as the solvent.

The recovered butenes may be returned to the P o ysis step- Similarly, fractionation, solvent extraction or azeotropic distillation may be employed in addition to the sulfone process described in Figure 8 to recover isoprene and piperylene from the stream flowing through pipe I I0.

The following examples are cited for purposes of illustration only to show about the yield of products obtained from pentene-2 and trimethylethylene when pyrolysed under conditions as disclosed in my invention.

Products of Pyrolysis of pentenes Example No.

Hydrocarbon charged Pentene fl. Pentenaz. z-Me-butene-ll (trimethylethlene). Average temperature... 760 (in... 777 0 813 Total ressure(mm.)..... 745 745 Time Sec.) 0.

0. volume ratio. Percent is weight of hydrocar n reacted during the ass. Reitaction v ocity conants. Yield C4Hs based on all: reacted, percent b wegbt. Yied 11 based on 51110 reacted, percent by weight.

Composition of products (wfiight percent):

1 Difference in total and 100.0 is the co and co, found In the effluent BBS.

The cracking conditions used may be governed by the following considerations.

In the case of a feed to the cracking unit consisting essentially of or comprising largely pentene-Z, the time-temperature relationship to obtain from 20 to 70 per cent cracking per pass is determined by the following Equation 1.

log t= When dealing with a feed to the cracking unit comprising mainly or consisting essentially of trimethylethylene, the most useful range is 15 to 50% converted per pass. The following Equation 2 covers the time-temperature relationship covering this region:

log 13.sss=0.31 The exact amount of decomposition selected feed to the unit (including any recycle) predominates, i, e. contains more than 50%, in pentene- 2, then conditions for that unit will be selected in accordance with Equation 1 above-for pentene- 2. If it predominates in trimethylethylene, conditions selected in accordance with Equation 2 will be used. For mixtures, I may use two stage cracking as described in the above-identified copending application of H. J. Hepp.

- Since the invention may be practiced otherwise 10 than as specifically described herein, and since various modifications and variations of it will be obvious to those skilled in the art, it should not be restricted except as specified in the appended claim.

I claim:

The process for the production of isoprene from trimethylethylene which comprises subjecting a feed stock comprising trimethylethylene to pyrolysis in a reaction zone at a temperature within the range of 750 to 850 C. at substantially atmospheric pressure for a period of time within the limits of the following equation:

where t is the reaction time in seconds and T is the temperature in degrees Kelvin, whereby from 15 to 50 per cent of the trlmethylethylene content of the feed is reacted with the production of isoprene.

FREDERICK E. FREY. 

